Sun Valves

Henry R. Bungay

Abstract:

One hundred years ago, sun valves were being employed throughout the world, and their inventor had been awarded a Noble Prize. Today few chemical engineers have even heard of them. As a low-cost, self-powered device, there are some obvious applications for sun valves, the most exciting of which is for algal farming.

Let's start by confessing that anything that a sun valve can do can be done as well or better with photocells, logic circuits, and control valves, but at ten to one hundred times the cost.

In 1912, the Swedish inventor Nils Gustaf Dalén was awarded a Nobel Prize for inventing a sun valve [1]. Prior to the 1930's when electricity took over, lighthouses throughout the world employed a Dalén sun valve to control the gas for the flame for the beacon. The Dalén valve simply turned on or off illuminating gas. The concept is simple. A system of rods has one blackened to absorb solar irradiation more efficiently while other rods are polished to reflect light, and the blackened rod expands more when warmed by sunlight to obstruct the flow of gas. Not much relative movement was possible with metals; inexpensive plastics now have much greater coefficients of thermal expansion and can provide control that is a function of the intensity of irradiation.

Material

Linear Temperature Expansion Coefficient (10-6 m/(m K)

ABS (Acrylonitrile butadiene styrene)

73.8

ABS (Acrylic

75

Aluminum

22.2

Brass

18.7

Copper

16.6

Iron, cast

10.4

Steel Stainless Austenitic (310)

14.4

Polyethylene

108

Polystyrene

70

Ref: http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html
Table 1. Coefficients of linear thermal expansion for some common materials.

The clever solution by Dalén to minimize the effect of ambient temperature was to use rods that were identical except for the coatings. Otherwise, the valve would respond to both ambient temperature and to solar irradiation in a complicated fashion. When the materials are identical, expansion due to warming by the sun greatly dominates over the effect of ambient temperature.

The Dalén valve turned gas off when the sun came up, but many applications need the valve to open instead. Selecting the desired action is illustrated in Figure 1. The red dots indicate that a component is attached to the mounting frame. Yellow indicates a clamp that is free to move with respect to the mounting frame and that connects to both the black expandable element and its reflective counterpart. In Sketch A, one end of the black element that expands when exposed to the sun connects to the stem of a valve fixed in place. When the sun shines, this arrangement shuts off the flow.
Fig. 1. Opening or Closing a Sun Valve
Sketch B show how to connect to open the valve when the sun shines. Expansion of the black element lifts the valve stem to increase flow.

Where can you get a modern sun valve?

A search using the key words "sun valve" came up with http://kim.oyhus.no/SunValve/ for a transparent plastic device that is incorrectly called a "sun valve". It allows radiation from the sun to enter during the day but keeps heat inside at night. No other relevant web pages were found.
A common gate valve or globe valve cannot simply be converted to a sun valve by attaching the expanding actuator to the valve stem because of the handle and threads. Valve manufacturers could quote on special orders for designs without handles and threads for the screw mechanisms as in Figure 2 but would have no expertise for the actuators and for mounting them.
Fig. 2. Gate Valve Modification Globe Valve Modification

In each sketch, the handle has been replaced by a connecting ring, and the screw system to advance or retract the stem is gone.
Converting a commercial control valve by removing its actuator and substituting a homemade actuator with plastic elements would be relatively easy but would sacrifice the cost advantages of a simple sun valve. What is needed is sufficient demand for sun valves such that companies could expect a return on investment by offering a new line of products in various sizes, and there is fortunately one potential application that might employ thousands of sun valves.

An algal farm can cover several hectares with hundreds of photobioreactors (devices for collecting sunlight to power a biological process). Valves for photobioreactors should not risk using brass or bronze because many organisms do not tolerate copper.
At night when there is no photosynthesis, algal farms need neither gas that provides carbon dioxide nor flow of nutrient medium. The costs of both equipment and labor for adjusting flows can be reduced markedly by using sun valves instead of valves that require human operators or expensive automatic controls.
Each unit has piping and valves. Labor cost is not trivial for adjusting these valves manually to accommodate night and day conditions and to match flow rates to intensity of solar illumination [2].

Routine chemical engineering with off-the-shelf components can set precise flow rates by placing a control valve for the gas (usually air but better if enriched with carbon dioxide) to each photobioreactor and another control valve on the line for supplying nutrient medium. With light sensors and a computer to calculate the flow rates, we have an elegant but too expensive solution. Although automatic valves can save labor, they require electrical or pneumatic systems with high costs to purchase and to install. A sun valve actuates itself.

Instead of fastening the gas valve and the valve for nutrient medium together to employ one common actuator, it is wise to consider a dual sun valve as in Figure 3. This is a top view of a block that has been drilled to form two tees side-by-side. Components in red are off-the-shelf pipes or pipe plugs, and plastic would allow easy drilling and taping of threads of the housing (blue). The ends of the metal stems are threaded to accept common faucet washers fixed in place by nuts of appropriate size at each side of a faucet washer. The pipe plugs on the other side are drilled to let the stems pass through and have O-ring seals secured by flat washers jammed into the plastic pipe plug. The clamp that connects to both stems should be metal to accommodate set screws that are unlikely to be readjusted after the initial positioning for setting valve properties. This element with the set screws permits matching the gas valve and the medium valve such that they open at the same time, and the set screw for the end of the actuator is for adjusting the action to start opening the valve when the sun comes up.
Fig. 3. Dual Sun Valve

Conclusion: If sun valves were commercially available, chemical engineers would find applications for them, especially in situations where electrical or pneumatic control valves are not practical. The goal of inexpensive renewable biofuels currently is beset by daunting hurdles of high projected capital costs and labor costs. Sun valves could well be crucial to economic fruition.